Precoding technology is applied more and more widely in wireless communication systems. Precoding technology is such that data is first precoded for channel loss compensation and then sent for better adapting to channel conditions, whereby the data transmission quality and/or throughput is improved.
At present, precoding technology can be divided into two categories. Take downlinks as an example. One category is such that a serving base station of a mobile terminal obtains channel information on a downlink multi-input multi-output (MIMO) channel through pilot signals and so on, and then the serving base station calculates a precoding matrix and sends data subsequent to precoding the data. The other is a codebook-based precoding method wherein a mobile terminal obtains channel information on a downlink MIMO channel through downlink pilots, preambles or midambles sent by a base station, then selects an index of the optimal precoding matrix from a codebook comprising a plurality of precoding matrixes and feeds the index back to a serving base station that sends data subsequent to precoding the data.
The issue of codebook construction is quite important in codebook-based precoding methods. There are currently two categories of codebook construction methods. One category is unstructured codebook construction, and the other is structured codebook construction. Generally speaking, a structured codebook is more popular in terms of lower construction complexity, better scalability and performances than an unstructured codebook. Description is presented to the construction of a structured codebook in the documents DFT based codebook (B. M. Hochwald, et al. ‘Systematic design of unitary space-time constellations’, IEEE Trans. Information Theory, Vol. 46, No. 6, 2000), Householder based codebook (IEEE C802.16e-04/527r4, ‘Improved feedback for MIMO precoding’, Intel, IEEE 802.16, Nov. 12, 2004) or Givens transformation based codebook (R1-070728, ‘Proposed way forward on codebook design for E-UTRA’. TI etc., 3GPP TSG RAN WG1 #48, February 2007).
However, the complexity, scalability and performance of the structured codebook depend on the number of transmit antennas; the larger the number of transmit antennas or base stations, the worse the flexibility of the structure codebook construction. Therefore, there is a need for a better codebook construction method to adapt to the increasing number of transmit antennas or base stations and precode data using the codebook.